The present invention relates to antennas, and more particularly, to miniature antennas that operate within the high frequency range and with relatively large signal currents.
In the prior art, short monopole antennas are used in a variety of circumstances to produce omni-directional low angle radiation patterns. Such antennas, however, require high voltage to produce the necessary current flow and characteristically have a high driving point impedance. Capacitive top loading may be employed to reduce the high voltage, lower the antenna impedance, and increase current, but the same is implemented at the expense of a more complex and larger antenna configuration which becomes limited in use and versatility. Since the generation of high voltages create problems related to efficiency, shielding, and insulation of such antennas, there is a need in many environments for a monopole antenna which can utilize low voltages yet still be provided in a configuration having compact design.
In the aforementioned co-pending application which is herein incorporated by reference in its entirety, a current enhanced monopole radiation type antenna is disclosed which overcomes many of the above-noted limitations. In particular, the application discloses a monopole and dipole antenna formed by creating an antenna from a loop current carrying conductor which has an unshielded radiating portion and a shielded non-radiating portion. A single loop forming a monopole antenna or plural loops forming dipole antennas may be coupled in accordance with the teachings in the aforementioned application to produce enhanced radiation which utilizes lower voltages in a more compact configuration. It has been discovered, however, that although the antenna constructed in accordance with the above-noted teachings produces an improved structure over prior art antennas, there is still a need for further improvements in the particular techniques of shielding and to enable operation of the antenna over a variety of frequency ranges. One example of the recognized need for such shielding and examples of problems associated therewith may be found with reference to the article "Antennas for Nonsinusoidal Waves", published in IEEE Transactions on Electromagnetic Compatibility, Vol. EMC-25, No. 1, Feb. 1983.
Accordingly, the present invention has been developed to overcome the specific shortcomings of the above known and similar techniques and to provide an improved miniaturized high frequency antenna.